With rise in temperature, the Young's modulus of elasticity

We need to determine how Young's modulus changes with temperature.

What is Young’s modulus? Young’s modulus ($$Y$$) is a measure of the stiffness of a material defined as the ratio of stress to strain within the elastic limit: $$ Y = \frac{\text{Stress}}{\text{Strain}} = \frac{F/A}{\Delta L/L} $$. It quantifies how much a material resists deformation under an applied force.

Effect of temperature on interatomic bonds: Young’s modulus depends on the strength of interatomic bonds, and as temperature increases, atoms vibrate with greater amplitude about their equilibrium positions. This increased vibration causes thermal expansion, increasing the average interatomic distance. Consequently, the interatomic forces become weaker because the atoms are, on average, further apart and lie on a flatter part of the potential energy curve. Since the restoring force per unit displacement decreases, the material becomes less stiff.

Therefore, Young’s modulus decreases with increasing temperature.

The correct answer is Option B: decreases.